The invention relates to a method and apparatus for assembling a fuel cell stack.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92 at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O at the cathode of the cell.
Because a single fuel cell typically produces a relatively small voltage (around 1 volt, for example), several fuel cells may be formed out of an arrangement called a fuel cell stack to produce a higher voltage. The fuel cell stack may include different plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite material or metal (as examples) and include various channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. The PEM may be part of a membrane electrode assembly (MEA), an assembly in which the PEM is bonded to and between the anode and cathode. The anode and the cathode may be made out of a carbon cloth or paper material, for example.
Referring to FIG. 1, due to the large number (approximately 100, for example) of plates 6 in a fuel cell stack, the plates 6 may be assembled in substacks, called plate modules 5, so that the fuel cell stack may be formed and tested one plate module 5 at a time. In this manner, each plate module 5 may be assembled and leakage tests may be performed on the plate module 5 before the plate module 5 is stacked onto other plate modules 5 at a stack assembly press (not shown).
During the testing and assembling of a particular plate module 5, it is important that components (plates 6, MEAs, gas diffusion layers (GDLs), gaskets, etc.) of the plate module 5 do not separate or slide relative to each other. In this manner, sufficient relative movement of the plates 6 and other components of the plate module 5 may compromise the sealing and performance of the plate module 5 and compromise the overall ease of assembling the fuel cell stack 10.
To assemble a particular plate module 5, dielectric glass rods 9 may be inserted into holes 8 in a bottom assembly plate 3 (used for assembly purposes only) so that the rods 9 extend in an upward direction from the assembly plate 3. Next the composite plates 6 may be stacked on top of each other in the appropriate order by extending the rods 9 through alignment holes 7 that are formed in the plates 6. Following the assembly and leakage testing of the plate module 5, the rods 9 are removed from the plate module 5, and the plate module 5 is transported to the stack assembly press to be combined with other plate modules 5. If the rods 9 prematurely fall out of the plate module 5, relative sliding or separation of its plates 6 (or other components) may occur.
Referring to FIG. 2, at the stack assembly press, long vertically extending dielectric glass rods 11 are extended through the alignment holes 7 of the plate modules 5 to align the plate modules 5. When all of the plate modules 5 have been slid over the rods 11, the plates 6 of the stack 10 are compressed by a compression mechanism (not shown in FIG. 2). The rods 11 typically remain in the fuel cell stack 10 when the stack 10 is compressed to keep the plates 6 aligned. If the plates 6 experience sufficient relative movement side to side, the passageways that are provided by the alignment holes 7 may become blocked or reduced in size enough to prevent the plates 6 from freely sliding over the rods 11. As a result, the plates 6 may become attached to the rods 11 during compression of the stack 10, an attachment that may cause the plates 6 to shatter.
In one embodiment of the invention, a fuel cell plate module includes fuel cell plates, a pin and a mechanism to hold the pin in place. The plates are arranged in a stack and include a first set of holes, and the pin extends at least partially through the first set of holes to align the plates.
In another embodiment, a fuel cell plate module includes fuel cell plates and a pin. The plates are arranged in a stack and include a first set of holes. A shaft of the pin extends through the first set of holes to align the plates. An extension of the pin radially extends from the shaft and is secured between an adjacent pair of the plates to hold the pin in place.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.